1. Field of the Invention
The present invention relates to a method of encoding a digital image with a verification data, and relates to a method and apparatus for decoding an encoded image to determine whether an alteration to the original image is effected in accordance with the results of the decoding. Further, the present invention relates to a computer readable medium storing program codes causing a processor to perform the decoding of the encoded image.
The technique for performing the decoding of an encoded image promises to play an important role in several fields, for example, the protection of confidential images and other intellectual property, distributed to the consumers, which helps prevent illegal alteration or intentional corruption of the original image.
2. Description of the Related Art
In recent years, with the advent of digitization of images and digital image distribution by using digital cameras or scanners, there are trends to substitute digital images for photographic images. Copyright protection of such digital images has become a substantial issue for image publishers and authors. For this reason, there is an increasing demand for establishing the technique for ensuring the copyright protection and distinguishing, from the real original image, forged images or the like that may be intentionally corrupted, illegally altered, or distributed via transmission channels by the third party.
One technique used to identify digital image ownership is a digital signature. Generally, in the digital signature technique, the signature information is produced from the data to be verified. This signature information is recorded onto a portion of an image file or another file as its attachment. Upon verification, the signature information is reproduced from the image data, the reproduced information is compared with the recorded signature information, and it is determined whether the image data is the real original image based on the result of the comparison.
However, the digital signature technique requires recording the signature information onto an image file as its attachment, and only a special file format can be used for this purpose. Further, the digital signature technique may be used only to determine whether the image data is the real original image, but it may not be used to identify which portion of the image is altered from the original image when the image is determined as not the original image.
Another technique used to identify digital image ownership is a digital watermark that is encoded or embedded into an image or image sequence. Such watermarks must be secure, robust to intentional corruption and to compression processing, and not unreasonably complex to encode and decode. The watermark is generally invisible to a viewer.
Japanese Laid-Open Patent Application No.11-98344 discloses a technique for detecting illegal alteration of a digital image by using electronic watermarking. In the method and apparatus of the above document, an original image and its corresponding watermark are registered into a management device. A synthetic image that is suspected to be an illegal alteration of the original image is compared with the original image registered in the management device to calculate a difference between the suspected image and the original image. A watermark is extracted from the calculated difference. The extracted watermark is compared with the watermark registered in the management device. When a match does not occur, it is determined that an alteration to the original image is effected in the suspected image.
However, the watermarking technique of the above document requires registering the original image and the watermark into the management device, and it is difficult to put the method of the above document into practical use.
An object of the present invention is to provide a verification data encoding method that effectively verifies the identification of digital image ownership without limiting the type of the digital image.
Another object of the present invention is to provide an original image verification method for determining whether an alteration to the original image is effected based on the result of decoding of an encoded image, which method effectively verifies the identification of digital image ownership and simply identifies which location of the image is altered from the original image when the image is determined as being altered from the original image.
Another object of the present invention is to provide an original image verification apparatus for determining whether an alteration to the original image is effected based on the result of decoding of an encoded image, which apparatus effectively verifies the identification of digital image ownership and simply identifies which location of the image is altered from the original image when the image is determined as being altered from the original image.
Another object of the present invention is to provide a computer readable medium storing program code instructions causing a computer to execute the original image verification method, which effectively verifies the identification of digital image ownership and simply identifies which location of the image is altered from the original image when the image is determined as being altered from the original image.
The above-mentioned objects of the present invention are achieved by a method of encoding a digital image with a verification data, the digital image containing a plurality of pixels, the method comprising the steps of: providing a verification data for each of the plurality of pixels, in order for determining whether an alteration to the digital image is effected; and inserting the verification data to each of the plurality of pixels of the digital image such that the verification data is invisible.
The above-mentioned objects of the present invention are achieved by an original image verification method for determining whether an alteration to an original digital image is effected based on a result of decoding of an input digital image, the input digital image containing a plurality of pixels, the method comprising the steps of: inputting a key information; providing a pseudo-random code by taking the pseudo-random code from a sequence of pseudo-random codes initialized by the key information; calculating a verification data through a predetermined operation based on a pixel value indicated by a predetermined number of bits of the pixel of concern in the input digital image and based on the pseudo-random code; and determining whether a value of the verification data matches with a value of the pixel of concern in the input digital image, in order to determine whether an alteration to the original digital image is effected, based on a result of the determination.
The above-mentioned objects of the present invention are achieved by an original image verification apparatus for determining whether an alteration to an original image is effected based on a decoding result, the apparatus comprising: a key input unit which inputs a key information; a pseudo-random code generator which provides a pseudo-random code by taking one of pseudo-random codes in a sequence initialized by the key information; a verification data calculation unit which calculates a verification data through a predetermined operation based on a pixel value indicated by a predetermined number of bits of the pixel of concern in the input digital image and based on the pseudo-random code; and a determination unit which determines whether a value of the verification data matches with a value of the pixel of concern in the input digital image, in order to determine whether an alteration to the original digital image is effected, based on a result of the determination.
The above-mentioned objects of the present invention are achieved by a computer readable medium storing a program of code instructions executable by a computer to perform an original image verification method to determine whether an alteration to an original digital image is effected, based on a result of decoding of an input digital image, the original image verification method comprising the steps of: inputting a key information; providing a pseudo-random code by taking the pseudo-random code from a sequence of pseudo-random codes initialized by the key information; calculating a verification data through a predetermined operation based on a pixel value indicated by a predetermined number of bits of the pixel of concern in the input digital image and based on the pseudo-random code; and determining whether a value of the verification data matches with a value of the pixel of concern in the input digital image, in order to determine whether an alteration to the original digital image is effected, based on a result of the determination.
In the verification data encoding method of the present invention, the verification data, provided for determining whether an alteration to the original image is effected, is inserted to each of the plurality of pixels of the image in such a manner that the verification data is invisible. Accordingly, the verification data encoding method of the present invention is effective in verifying the identification of digital image ownership without limiting the type of the digital image. Further, the original image verification method and apparatus of the present invention are effective in verifying the identification of digital image ownership, and make it possible to simply identify which location of the image is altered from the original image when the image is determined as being altered from the original image. It is not necessary to register the original image and the verification data in a memory of a system that performs the original image verification. The original image verification method and apparatus of the present invention do not depend on a special file format as in the conventional digital signature technique.